Circuitry for use with a transducer which generates a signal corresponding to a physical phenomenon

ABSTRACT

The present circuit is primarily designed to be employed with a transducer which generates a signal in response to some physical phenomenon and said present circuit provides a direct current signal which is an excellent representation of the intensity of said physical phenomenon. In addition said circuit has excellent response over a broad frequency range as related to said physical phenomenon and has high signal to noise ratio. The present circuit principally utilizes a low pass filter which provides a relatively flat response at all frequencies below one-half of the carrier frequency as well as employing a notch filter designed to filter signals at twice the carrier frequency. The twice filtered signal is a low ripple direct current signal having the earlier described characteristics.

CROSS REFERENCE

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 264,781 entitled "Torque Measuring and ControlSystem" filed June 21, 1972 which has now issued as U.S. Pat. No.3,858,443 on Jan. 7, 1975.

BACKGROUND

The present invention relates to a circuit to be used with a transducerto generate a well defined direct current signal in response to thetransducer output and said circuit as described in particular as it isused with a device to measure extraordinary torque and which generatessignals to control and/or monitor the torque generating means inresponse thereto.

In many technical applications shafts are employed to rotate andtransmit power from one place to another. For instance, in bolting partsof an automobile together, the bolts must be sufficiently "tight" sothat they will not vibrate loose when the automobile is in operation onthe road. This requirement means that a sufficient amount of torque mustbe applied to a bolt to turn it beyond a simple bottoming out point tobecome a "tight" bolt. On the other hand the driving must not apply somuch torque beyond the bottoming out position that the bolt head getssheared or the bolt threads get stripped. While it has very often beenthe practice to provide a clutch on the shaft or to use a soft pinthrough the shaft being rotated, such arrangements require severelimitations of the applied power. The clutch must be spring-loaded insome fashion; and when the torque exceeds the permissible value, theclutch disengages. Such arrangements are not very exacting nor are theyquickly responsive. The soft pin technique of course requires that thesheared off pin be driven from the shaft and replaced upon the occasionthat the shaft has experienced an excessive amount of torque and the pinhas sheared.

SUMMARY

In the preferred embodiment the present system employs a torquetransducer which has a pair of flanges each of which has an aperturetherein. The transducer has a first flange which may be considered thefixed flange and has a second flange which may be considered the forceflange. In between the fixed flange and the force flange is a tube orhollow shaft which enables the shaft transmitting the power to passtherethrough. The force flange has means which enable it to be securedto the housing of the source of power, for instance a motor, which isdriving the shaft providing the torque. The fixed flange has means toenable it to be secured to a relatively stable means, such as a heavyframe holding the entire structure or a wall. The stable means need onlybe a means which will not respond to any reaction of the power source.Mounted on the fixed flange is a pair of sensor supports each of whichholds a pair of E-coils. The force flange supports a pair of vaneholders upon each of which there is mounted a piece of metal having highpermeability to magnetic flux and called a vane. Each of the vanes isdisposed between an associated pair of E-coils. When the force flangeexperiences a twist or torque with respect to the fixed flange the vanesupports move and the associated vanes are displaced to be in closerproximity to one or the other of said E-coils. The uneven displacementprovides the basis for a dissimilarity and an electrical signal.

Heretofore strain gages have been employed to provide an output signalwhich is representative of such a torque, but strain gages are limitedby low amplitude output signals. In contrast an E-coil with a vanearrangement as just described provides a high amplitude output signalbut that advantage is often lost with the generation of an equivalentlyhigh noise. To overcome the conflicting characteristics of highamplitude output accompanied by high noise, special circuitry isemployed which is the subject of this continuation in part.

The E-coils are electrically connected in a bridge circuit and theoutput of the bridge circuit is subject to a full wave demodulation toproduce a pulsating D.C. voltage with a fundamental ripple frequency oftwo times the carrier frequency. The pulsating D.C. signal is passedthrough a notch filter which is designed to filter a signal having afrequency of twice the carrier signal which in turn provides a lowripple D.C. signal whose voltage level is an excellent representation ofthe difference in the torque between the force flange and the fixedflange.

The objects and features of the present invention will be betterunderstood in accordance with the description below taken in conjunctionwith the drawings wherein:

FIG. 1 is a pictorial schematic of a front view of the transducercoupled to a motor driven bolting device;

FIG. 2 is a pictorial schematic of a side view of the transducer per se;

FIG. 3 is a top view of the transducer shown in FIG. 1; and

FIG. 4 is an exploded view of E-coil;

FIG. 5 is a partially schematic and block diagram of an electricalsystem which can be used with the present transducer;

FIG. 6 is a vector diagram showing the signals present in the initialpart of the circuitry of FIG. 5;

FIG. 7 is an embodiment of the details of the circuit which can be usedas the circuitry shown in the block portions of the diagram of FIG. 5.

FIG. 8 is a presentation of an unfiltered demodulated signal as itappears on line 100 of FIG. 7;

FIG. 9 is a representation of a demodulated signal after it has passedthrough the low pass filter;

FIG. 10 is a representation of a demodulated signal after it has passedthrough the low pass filter as well as the notch filter;

FIG. 11 is a representation of the signal of FIG. 9 and its relationshipto a threshold signal with which it is compared, and

FIG. 12 is a representation of the relationship between torque andoutput voltage for a conventional filter as well as for the presentsystem.

Consider FIG. 1 which shows a front view of the transducer of thepresent invention coupled to a motor driven bolting device. In FIG. 1there are shown flanges 11 and 12, each of which has six bolt holestherein, three of said bolt holes are depicted in phantom, the otherthree holes in each flange are not shown in FIG. 1. The holes 13 through18 are better seen in FIG. 3 which is a top view of the force flange 12.It should be understood that bolt holes 13, 14 and 15 can be eitherthreaded or not threaded. As can be seen in FIG. 1 there is a centertube or hollow shaft 19 which is rigidly secured between the flanges 11and 12. Also as can be seen in FIG. 1 there is a pair of sensor supports20 and 21 which are mounted on the fixed flange 11. In addition as canbe seen in FIG. 1 there is a pair of vane supports 22 and 23 which areshown mounted on the flange 12. The same identification numerals areused in FIGS. 2 and 3. In the Figures the vanes and sensors are shownexternal to the center tube 19; however, the ID of the hollow shaft 19could be large enough to house the vanes and sensor supports.

In FIG. 1, there is also depicted a motor 24 which has a coupling plate25 secured thereto. The coupling plate 25 has three threaded bolt holes26, 27 and 28 (shown in phantom) therein. The threaded bolt holes 26, 27and 28 match the bolt holes 13, 14 and 15, and while it is not shown assuch (in order to keep the drawings simplified), it should be understoodthat the force flange 12 is bolted to the plate 25. It can also be seenin FIG. 1 that the force flange 12 has a guide plug 29 (shown in phantomin FIG. 1, but which can be seen in FIG. 3). The guide plug 29 fits intothe plate 25 and aligns the bolt holes as well as the center apertures30 and 31. The center aperture 30, (in the plate 25) and center aperture31 (the hollowed out portion of center tube 19) when aligned permit thedrive shaft 32 to pass therethrough. The drive shaft 32 is part of themotor 24 and is the means by which torque is delivered to the bolt 33.The drive shaft 32 is equipped with an hexagonal cup into which thehexagonal head of the bolt 33 is inserted.

In FIG. 1 the bolt 33 is depicted as being threaded or screwed downwardin order to bolt the plate 34 to the support 35. Plate 34 and support 35could be sections of an automobile, airplane, boat or the like. Itshould be borne in mind that the motor 24, shaft 32, bolt 33, plate 34and support 35 are not part of the present invention but are merelyoffered to help teach the invention.

One other item should be noted in FIG. 1; i.e., that the fixed flange 11is secured to a reference means 36. The reference means 36 can be aportion of a heavy frame, a motor housing, a wall or some means uponwhich there is very little or no effect in response to the reaction ofthe motor 24 when the bolt 33 bottoms out.

Consider FIGS. 1, 2, and 3 together and consider that the motor 24 isdriving the shaft 32 which in turn is tightening the bolt 33. When thehead of the bolt 33 abuts the plate 34, the bolt will resist any furtherclockwise rotation and the motor will react by attempting to rotatecounterclockwise (obviously if the bolt 33 is threaded with a left-handthread the directions are opposite from those just described) as shownin FIG. 3 by vector 37. The motor is secured, through plate 25 to forceflange 12. Therefore as the motor attempts to twist the bolt 33clockwise, it moves around counterclockwise on shaft 32 and hence twiststhe force flange 12 in a counterclockwise direction. Even though theforce flange 12 is coupled to the fixed flange 11 by virtue of thecenter tube 19, the fixed flange 11 will not move since it is secured tothe reference means 36.

Accordingly, if we consider FIG. 1, the vane support 22 would be movinginto the drawing while the vane support 23 would be moving out of thedrawing. When the vane 22 moves, as though it were into the drawing, thevane 38 moves away from the E-coil 39 toward the E-coil 40; therebyincreasing the reluctance for magnetic flux being developed in theE-coil 39. Therefore, a difference of electrical impedance between theE-coils 39 and 40 is developed. While E-coils are discussed herein, itshould be understood that many electromagnetic devices such as U-coils,etc. could be used.

The flanges 11 and 12 are made of 410 stainless steel, which has beensuitably heat treated, while the center tube 19 can also be made ofstainless steel. The vane supports 22 and 23 are fabricated fromnon-permeable material, such as 303 stainless steel, while the sensorsupports 20 and 21 are fabricated from the same non-permeable material.

It should be noted in FIG. 2 that there are shown lead-in wires 41 and42 which enable the signals to be applied to the E-coils and whichenable signals developed by the E-coils to be transmitted to some otherlocation. It should be understood that there are a pair of E-coils lyingopposite the E-coils 39 and 40 which are mounted on the support sensor21 and which cannot be shown or seen in FIG. 2.

In FIG. 4 there is shown an E-shaped yoke 43 which is representative ofthe E-shaped yokes which make up part of the assembly referred to asE-coils, such as E-coils 39 and 40. Also in FIG. 4 there is shown a coil44 which has an aperture 45 therein which fits over the E-shaped yoke 43to form an E-coil of the type referred to as E-coils 39 and 40. When asignal is applied to the E-coil 44 assuming that the coil 44 is mountedon the E-shaped yoke 43, magnetic flux will pass through the center stemof the E-shaped yoke and out through the upper and lower ends and backinto the center stem. The magnetic flux passing out the ends of theE-shaped yoke and returning to the center piece will have to passthrough air which has a relatively high impedance to magnetic flux. Ifthere is a vane, or a metal piece, which is fitted over the end piecesas well as the center piece then the magnetic path or flux pathexperiences a low impedance. Hence, when an electrical signal is appliedthere is more back EMF generated and the electrical signal experiences ahigher electrical impedance. This is the principle with which thetransducer is employed.

Accordingly in our example, shown in FIG. 1, as the force flange 12moves counterclockwise the vane 38 moves closer to E-coil 40 providing ahigher electrical impedance thereat than an electrical signal isexperiencing at E-coil 39. On the other hand the vane 46 moves close toE-coil 47 to provide a high electrical impedance thereat as comparedwith the other coil 49 (not shown) on the left-hand side of FIG. 1. Thisimbalance of electrical signal is transmitted on lines 41 and 42 and isproportional to the amount of torque experinced by flange 12 withrespect to flange 11.

Consider FIG. 5 which is a partial schematic block diagram of oneembodiment of circuitry which in fact makes the transducer of the typeabove, or other transducers such as strain gages, that may utilize acarrier frequency for operation, into a superior device for themeasurement of torque. In FIG. 5 there is depicted an a.c. source 48which provides an a.c. signal to the coils 39, 40, 47 and 49 of bridge50. The coils 39 and 40 in FIG. 5 are representative of the E-coilsshown in FIGS. 1 and 2. Although there are no keepers or vanes shown inFIG. 5 it is to be understood that the coils 39, 40, 47 and 49 areE-coils mounted on a transducer similar to the transducer shown in FIGS.1, 2 and 3. It should also be understood that the coils 39, 40, 47 and49 have associated vanes that are moved as described earlier toinfluence the flux path of the flux generated by these last-mentionedcoils.

An a.c. signal is supplied from the a.c. signal source to the lines 51and 52. Across the lines 51 and 52 there is connected a bridge circuit50 comprising the four coils 39, 40, 47 and 49. The four coils 39, 40,47 and 49 are connected in the classical bridge configuration. When thevanes are moved the coils which lie opposite to one another are affectedsimultaneously. By way of example, when the vanes are moved as describedearlier the electrical impedance of the coil 40 is increased andsimultaneously the electrical impedance of the coil 47 is increased. Ina like fashion, when the vanes are moved in the opposite direction, theelectrical impedance of the coil 39 is increased and simultaneously theelectrical impedance of the coil 49 is increased.

When the bridge is in its neutral position, that is, when the keepersare not moved in any direction, such as under circumstances when thereis no torsion being measured, ideally there should be no output signalat the terminals 53 and 54. Unfortunately the coils are never fabricatedperfectly; i.e., the impedance of the coils do not match. Hence, anapplied signal under no load conditions finds an unbalanced bridge, notonly in an impedance sense, but in phase relationship sense and thisunbalance results in an error or an output signal at the terminals 53and 54. In order to correct or effectively remove this no load outputsignal, two signals are added. A phase correction signal is added to thebridge output signal and in addition there is an amplitude correctionsignal added. Both of these correction signals are out of phase with theapplied signal and as will be apparent hereinafter their summation willnullify or effectively "wipe out" the no-load output signal.

The nullification of the no-load output signal can be better understoodif we consider FIG. 6 wherein we find that the reference signal (that isthe signal from the a.c. signal source) is represented by the vector 55.We also find in FIG. 6 that the no-load output signal from the bridge 50can be represented by the vector 56. Note that the no-load output signal56 has a phase shift from the applied signal 55. Vector 56 in FIG. 6 isarbitrarily chosen and can vary at an angle and length depending uponwhat the mismatch is between the impedance and the phase of the E-coils.In order to nullify the signal represented by vector 56 the system mustgenerate a signal whose amplitude is equal to the vector 56 and whosephase is 180° from the vector 56, this signal is represented by thevector 57. The generation of the signal 57 is accomplished by generatingone signal represented by the vector 58 and a second signal representedby the vector 59. It will be noted that there is connected across thelines 51 and 52 a capacitor 60, a resistor 61, and a capacitor 62. Thisarrangement will give a 45° to 90° phase shift to a signal at the tap ofthe resistor 61, which signal is added to the output signal appearing atthe terminals 53 and 54. The signal appearing at the tap of the resistor61 as shown by the vector 58. Actually the vector 58 need not be a 90°signal and this would depend upon where the tap is located on resistor61. The signal 58 however would be at some angle very close to 90°.Nonetheless the signal appearing at the tap of the resistor 61 wouldhave a component which would be 90° to the reference signal 55.

Simultaneously with the generation of the 90° signal 58, the adjustableresistor 63 is adjusted until there is no bridge output signal appearingat the lines 64 and 65. This accomplished by the signal 59 which is 180°out of phase with the signal 55 and the vectorial addition of thevectors 58 and 59 provides the signal 57 which nullifies the no-loadoutput signal 56. It should be understood that the generation of signal59 is accomplished by simply reading an oscilloscope or some other meansset up to read the output signal on lines 64 and 65 as the resistor 63is being adjusted. When there is no output signal for the no-loadcondition then the variable resistor 63 has been adjusted to the properlocation.

Now it should be borne in mind that while there have been out of phasesignals added to nullify the no-load output signal this correction doesnot eliminate the phase shift which takes place between the appliedsignal on lines 51 and 52 and the output signal appearing at the outputterminals 53 and 54 when the system is operating under a load condition.This will become more apparent hereinafter.

As was mentioned earlier when the transducer is experiencing anextraordinary torque condition the vanes will be moved toward one or theother set of coils of the bridge 50, that is toward coils 39 and 49, ortoward coils 40 and 47. In this situation, the electrical impedance ofthe coils toward which the keepers are moved will be increased and hencethere will be a potential difference across the output terminals 53 and54, thus providing an output signal. This output signal is the measureof the torque being experienced by the transducer under load conditions.The output signal will appear at lines 64 and 65 which are input linesto the difference amplifier 66. The output signal from the differenceamplifier 66 appearing on line 67 will be a sine wave whose varyingamplitude will represent the output signal from the bridge 50 as itappears at the terminals 53 and 54 and which will have a phase shiftfrom the reference signal due to the distributive capacitance of thebridge as well as the inductance present in the E-coils which make upthe bridge. As will be explained in more detail hereinafter thedemodulator 68 acts to convert its varying signal input into a pulsatingd.c. signal. The demodulator 68 is connected to receive the referencesignal on line 51 so that there results an output signal on line 69which is a pulsating d.c. signal whose amplitude represents thedifference signal transmitted on line 67 but whose frequency is twicethat of the reference signal applied on line 51. This pulsating d.c.signal is transmitted to the low pass filter 70 from whence there istransmitted a resultant output signal which is a d.c. signal having somecomponents at twice the reference signal frequency. In other words, thelow pass filter 70 impedes all signals which have a frequency greaterthan one-half the reference frequency. Thereafter the signal from thelow pass filter 70 is passed to a notch filter 71, which is a doublt Tnetwork whose parameters are chosen to attenuate a signal whosefrequency is twice the reference signal frequency.

The notch filter 71 serves to remove the signal component having afrequency of twice that of the reference signal from the d.c. output andthus to provide d.c. signal whose voltage level represents thedifference signal developed at the output terminals 53 and 54 of thebridge 50. The non-pulsating d.c. output signal from the notch filter 71is transmitted to the difference amplifiers 72 and 73. The amplifier 72can be considered as a low torque monitor which can cause some logiccircuitry to respond when the torque being monitored is below a certainlevel. On the other hand, amplifier 73 can be considered as a hightorque monitor in a comparison circuit which can cause some logiccircuit to respond when the torque being monitored is above a certainlevel. The output signals from the amplifiers 72 and 73 are generated bycomparing the non-pulsating d.c. signal from the notch filter 71 with aprecision reference supply signal. If, for example, the device is beingused to monitor a tool which was securing bolts in an automobile bodyframe and there is a known value of minimum torque which must be appliedto a bolt to keep it from vibrating loose when the automobile is inoperation then the representative value of voltage (i.e., a voltagevalue representing that minimum torque) would be applied on the line 74.Accordingly, if the torque applied, as represented by the output signalfrom the bridge 50, and as further represented by the output signal atthe notch filter 71, falls below the minimum value then the signal online 75 would be below the value of line 74 and an output signal on line76 would indicate an insufficient torque for safely bolting to parts ofthe automobile body.

On the other hand, if too much torque would overstress the bolts beyondsafe limits in our automobile example, then a maximum torque isdetermined and the applied torque must be kept below this maximum value.In order to monitor this upper limit of torque, an appropriate referencesignal is applied on line 77. This signal provided on line 77 wouldrepresent a torque which is less than the maximum torque but higher thanthe minimum torque. If the applied torque represented by the differencesignal from the bridge and further represented by the output signal ofthe notch filter, approaches the maximum value, the signal on line 78would exceed the signal on line 77 and the maximum amplifier 73 wouldhave an output signal. The maximum output signal would cause a logiccontrol circuit to terminate the bolting operation to prevent the boltfrom being sheared or simply warn the operator to terminate the boltingoperation.

A more detailed study of the circuits of the preferred embodiment can beseen in FIG. 7. In FIG. 7 the reference signal mentioned in connectionwith FIG. 5 is found on line 51 while the difference signal is found online 67. The reference signal found on line 51 is phase shifted byvirtue of the serial connection made up of the capacitor 79, theresistor 80, the capacitor 81, and ground. This particular arrangementwill phase shift the reference signal by a maximum of 45°. Since it hasbeen determined that the difference signal developed at the outputterminals 53 and 54 usually does not phase shift more than 20° from thereference signal, the possible adjustment of the phase shift of thereference signal to a maximum of 45° is sufficient. The tap on theresistor 80 is adjusted so that the reference signal is phase shifted tobe in phase with the difference signal on line 67. This is accomplishedbefore the device or circuit is put into use by putting some load on thetorque mechanism and reading the output signal from the operationalamplifier 82. When the output signal from the operational amplifier 82is at a maximum value then the position to which the tap of a resistor80 is set is the correct position.

As can be seen in FIG. 7, the reference signal which has now been phaseshifted is transmitted on the line 83 to the base elements of thetransistors 84 and 85. In accordance with this transmision, the signalis clipped by the diodes 86 and 87 so that the output signal from eachof the transistors 84 and 85 is an amplified output signal, having arectangular configuration, appearing at the collectors 88 and 89. Thetransistors 84 and 85 are turned on alternatively. The output signalsfrom the collectors 88 and 89 are further transmitted to the baseelements of the tannsistors 90 and 91, and in accordance therewith areclipped by the diodes 92 and 93. The twice amplified signals from thetransistors 90 and 91 are transmitted from their respective collectorson the lines 94 and 95 to the respective gate elements of the fieldeffect transistors 96 and 97. The field effect transistors 96 and 97 arecut off with a negative signal and are turned on when the positive goingsignal reaches "ground" level. Accordingly the field effect transistors96 and 97 will conduct when their gate elements are subjected to apositive signal (ground signal). Since the rectangular pulses from thetransistors 90 and 91 are generated alternately, i.e., 180° out of phaseit follows that the field effect transistor 96 and 97 are alternatelyrendered in a conducting condition. The field effect transistors 96 and97 will conduct in accordance with the amplitude of the differencesignal appearing on line 67 and in response to being subjected to aground potential signal at their respective gate elements. In accordancewith this operation the field effect transistor which is conducting willrender the input line to the operational amplifier at ground level,while the other input to the operational amplifier 82 will be at thelevel of the difference signal at line 67. To be specific, if the fieldeffect transistor 97 is conducting, the line 98 will be at groundpotential while the line 99 will be at the voltage value of thedifference signal on line 67. Accordingly, it becomes clear that thesignal applied across the input lines 98 and 99 of the operationalamplifier 82 is the difference signal and this difference signal isapplied at every half cycle of the reference signal so that it isapplied at twice the frequency of the reference signal or 2 f.c. Thevalues of the resistors and choice of transistors shown is not criticalbut were chosen to be used with a carrier frequency of 2500 Hz and aninput signal of up to 10 volts. The operational amplifier 82 can be anMC1439 monolithic integrated circuit, manufactured by Motorola and actsto produce a pulsating d.c. signal on line 100.

The pulsating d.c. signal 108 emanating from the operational amplifier82 is at twice the carrier frequency and is depicted in FIG. 8. Thedashed line 110 passing through the pulsating d.c. signal representationindicates the d.c. average level or in effect the signal levelrepresenting the actual torque. The pulsating d.c. signal on line 100(FIG. 7) does include unwanted harmonic signals. Hence, this pulsatingd.c. signal is transmitted to the low pass filter 70 whose parametersare chosen such that the harmonics are attenuated; i.e., so that onlyfrequency components within a desired bandwidth are passed. The valuesof the circuit parameters shown are for use with a reference signalfrequency of 2500 Hz. However, it should be understood that the valuesare not critical because they would depend on the reference signalfrequency and the design of such a filter is readily understood by thoseskilled in the art. The operational amplifier 101 can also be an MC1439described earlier. Hence, the signal emanating on line 102 is a d.c.signal of lower amplitude and containing some component at twide thecarrier frequency. The signal 112 appearing on line 102 is a d.c. signalof lower amplitude and containing some component at twice the carrierfrequency. The signal 112 appearing on line 102 is depicted in FIG. 9.In FIG. 9 it will be noted that the d.c. average 110 is at the sameamplitude as it was in FIG. 8. It should be noted that signal 112 inFIG. 9 is characterized by having a d.c. component which betterrepresents the difference signal on line 67 because it has had theharmonic signals removed. Thereafter this d.c. signal 112 appearing online 102 is transmitted to the notch filter 71, which is a double Tnetwork whose parameters are chosen to attenuate a signal whosefrequency is twice the reference signal frequency. The valves of thecircuit parameters are not critical because they would depend on thereference signal frequency and the design of a double T network isreadily understood by those skilled in the art. The double T network ofnotch filter 71 provides a low ripple signal 114 (FIG. 10) on line 103,whose voltage level represents the value or amplitude of the differencesignal. Hence, the low ripple signal on line 103 represents the changein position of the vanes, which in turn represents the amount ofextraordinary torque being applied for instance to the bolt in ourautomobile example. The low ripple signal 114 shown in FIG. 10 is a welldefined signal which can be considered a d.c. signal.

The d.c. signal on line 103 is transmitted to the operational amplifier104 wherein it is simply amplified for further use. The double T networkneeds a high impedance as a load in order to be able to operate at itsoptimum and the operational amplifier 104 provides that high impedanceload. It should be understood that this output signal appearing on line105 can be applied to any kind of logic to which any reference signal isalso applied, so that all types of monitoring arrangements can beemployed, as described earlier in the description of FIG. 5. In thepreferred embodiment the signal is stored whereby a fixed value can bedetermined and the peak value or torque can be displayed or furtherused.

If the signal representing the actual torque is not "tailored" to a lowripple or d.c. signal then an error could readily occur when such asignal is transmitted to a comparator. FIG. 11 provides a graphicillustration of this possibility. In FIG. 11 the once filtered signal112 is shown in an amplitude increasing mode (i.e. more torque is beinggenerated). As in FIGS. 9 and 10, the dashed line 110 represents theactual torque level or the analog signal of the actual torque. In FIG.11 there is shown the threshold signal 115 which is fed into acomparator such as difference amplifiers 72 and 73. If the (ripple)signal 112 has a relatively large "swing" then it will cross thethreshold signal at point 116 when actually the analog signal would notcross the threshold signal 115 until point 117. If signal 112 were a lowripple signal such as that shown in FIG. 9 then the crossover would beat approximately point 117.

If conventional methods of filtering are used to reduce the ripple thenthe number of low pass filters would be increased. Low pass filtersnormally employ capacitors with other components to effect theattenuation and the R-C networks that result therefrom create great timedelays. Such a technique results in a poor response to rapid changes inthe frequency of the input signal. Since the input signal is the analogof the physical phenomenon it would mean that the prior techniqueresults in a poor response to a rapid physical change such as a rapidchange in torque. Because there are only two stages of filtering and alarge amplitude input signal the present system provides an excellentresponse to rapid changes at the input, often referred to good transientresponse. FIG. 12 shows the relationship between an increase of actualtorque 118 with time, the resultant analog signal 119 which results fromconventional filtering and the resultant analog signal 120 when a systememploys the present circuit.

The present system has the advantage of a high level a.c. signal input;i.e. the system is not subject to general instabilities and drift whichaccompany d.c. input signal arrangements. In addition there is no limiton the total torque to be measured. The torque can be either high or lowand the only prerequisite to be met is by the size of the center tubethickness.

I claim:
 1. A circuit to be employed with a transducer which translatesa mechanical motion into an alternating current electrical signal whichincludes a carrier frequency signal whose amplitude is representative ofsaid motion, comprising in combination: amplifier means adapted to beconnected to said transducer to receive said alternating current signaland to generate an amplitude sinewave-like signal whose amplituderepresents a measure of said mechanical motion; signal demodulatingmeans connected to said amplifier means to receive said sinewave-likesignal and translate it into a pulsating direct current signal whichpulsating direct current signal includes a component having twice thefrequency of said carrier signal; low pass filter means connected tosaid signal demodulating means and formed to receive said pulsatingdirect current signal and to impede all signal components of saidpulsating direct current signal which have a frequency greater than apredetermined value including signals whose frequency is twice saidcarrier frequency thereby providing a once filtered signal; and notchfilter means connected to said low pass filter means and formed toreceive said once filtered signal and to attenuate that component ofsaid once filtered signal which has a frequency of twice said carrierfrequency thereby providing a non-pulsating direct current signal whosevoltage level is a reliable measure of said mechanical motion.
 2. Acircuit to be employed with a transducer according to claim 1 whereinsaid transducer includes a bridge circuit having first and second outputterminals and further includes a difference amplifier connected to saidfirst and second output terminals.
 3. A circuit to be employed with atransducer according to claim 2 wherein there is further included afirst adjustable circuit connected to said bridge circuit to correct fora no load phase imbalance in said bridge circuit and a second adjustablecircuit connected to said bridge circuit to correct for inherentcomponent mismatch to thereby balance said bridge under no loadconditions.
 4. A circuit to be employed with a transducer according toclaim 1 wherein said transducer has an alternating signal sourceconnected thereto and wherein said signal demodulating means has areference signal terminal and includes circuitry means connecting saidreference signal terminal to said alternating signal source to receive areference signal therefrom and a difference signal terminal connected tosaid amplifier means and wherein said signal demodulating means furtherincludes a phase shifting means and a first signal amplifier stageconnected to receive said reference signal through said phase shiftingmeans and a second signal amplifier stage connected to receive theoutput signal from said second signal amplifier stage.
 5. A circuit tobe employed with a transducer according to claim 1 wherein said notchfilter comprises: first and second resistors each having first andsecond ends and connected in series at their respective first ends andwith a first center terminal thereat; first and second capacitors eachhaving first and second ends and connected in series at their respectivefirst ends and with a second center terminal thereat; said firstresistor and said first capacitor connected in parallel at theirrespective second ends and having input signal means thereat; saidsecond resistor and said second capacitor connected in parallel at theirrespective second ends and having output signals thereat and, a thirdresistor and a third capacitor, each having first and second ends, saidthird resistor series connected to said third capacitor through theirrespective first ends with their respective second ends connected tosaid first and second center terminals.